NEWS ANALYSIS
IGBT inventor crusades wide bandgap semiconductors
As academic Jay Baliga from North Carolina State University steps up to lead the $140 million ‘Next Generation Power Electronics National Manufacturing Innovation Institute’, Compound Semiconductor asks about his past, plans and relentless pursuit of the power semiconductor.
Q A
You invented the silicon IGBT, have pioneered wide bandgap semiconductor devices, and you’ve just received the IEEE Medal of Honor. Where did this all start?
I invented the IGBT in 1980, the same year that I derived an equation that, for the first time, related resistance in power devices to material properties. I called it Baliga’s figure of merit. So when I discovered this, I also started looking for alternative semiconductor materials to silicon, and the first promising material I found was gallium arsenide. Working at GE at the time, we put together a group and developed the first wideband gap power device based on GaAs in 1985. We commercialised this and these devices are still available across the industry today.
Q A
At any point did you feel torn between the two competing technologies; silicon and wide bandgap semiconductors?
It was actually a pretty tough time for me as I was trying to develop the IGBT as quickly as possible and then I had to do the GaAs programme as well. But I had always seen wide bandgap
semiconductors as the future, although I had not appreciated how long it would take for wide bandgap semiconductor devices to become commercial. With the IGBT I commercialised it in a remarkable ten months, which was why it became so widely used in so many diverse applications from air cooling systems to drives and lighting. Thirty years has been a very long time, but wide bandgap semiconductors are now cannibalising on the IGBT, and this is how I always believed it would happen.
Q A
The first wider bandgap semiconductor you worked on was GaAs, what came next?
My equation predicted that with SiC, which has an even wider bandgap, I could get a 1000 fold improvement [in performance]. I’d predicted a 13.7 times improvement with GaAs, so this was another two orders of magnitude. When I found this one thousand fold opportunity, I started to look at how to make devices. But this was the early 1980s, and there was no SiC technology at the time. So we went to see Professor Robert Davis in the materials science and engineering department at North Carolina State University. He developed some growth processes for SiC wafers, and his
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students later spun off the company, Cree. Cree started to produce SiC wafers and this, as well as my interest in collaborating with Dr Davis, brought me to North Carolina from GE.
Q A
So what power devices followed? In 1991, I set up a power
semiconductor research centre at the university. This was, and is, an industrial consortium. With the funding that came from that consortium we made the first high performance SiC electronic devices. In 1992, we announced a very high performance Schottky rectifier and by 1995 we had developed a very high performance power MOSFET.
I do think these devices helped the industry appreciate this technology; these systems had proven the theory, so many programmes to develop more devices followed. By 2000 to 2005 we started to see a lot of products, particularly Schottky rectifiers and junction barrier Schottky (JBS) rectifiers based on an idea I proposed for silicon in the 1980s. These rectifiers were the first products and then we had power MOSFETs. Today, Infineon, Cree, Rohm and a whole bunch of companies now manufacture these SiC products.
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